How doesn't this part of the interaction even minimally violate the 2nd & the 4th Amendments in the Bill of Rights? Unless I missed it in the OP's responses, I don't remember reading that he gave up his right to possess his firearm, or his right preventing him from seizure of property? Unsure of the laws in SC regarding running a firearm's serial through their database, I can't really speak to the issue of that search. Just because the OP indicated that this was "a good encounter overall" doesn't mean that he wasn't deprived of his rights, much less whether any such deprivation was lawful.
The older guy opened my car door, gently grabs my left wrist, and tells me to get out of the car, and just keep my hands visible. I, of course, comply eagerly. Once I'm out of the car, he removes the gun from my pocket, and hands it over to the woman who goes over to the Tahoe and calls in the serial number. (It came back clean, of course) The older guy asks if he can search me, and the car. I kind of shrug and tell them I'm not hiding anything; and to go for it.